1. Field of the Invention
The present invention relates to a battery pack, and more particularly, to a battery pack included in a battery, for example, a smart battery, used in a portable electronic apparatus such as a notebook computer.
2. Description of the Related Art
FIG. 1 shows the wiring structure of a battery pack 11 of a conventional smart battery 1. FIG. 2 shows an equivalent circuit corresponding to the wiring structure of FIG. 1. FIG. 3 shows a resistance equivalent circuit corresponding to the wiring structure of FIG. 1.
Referring to FIGS. 1 through 3, the conventional smart battery 1 includes a smart circuit module 10 and the battery pack 11. A negative pole output terminal of the battery pack 11 is connected to a negative pole terminal (Bxe2x88x92) of the smart battery 1. Also, an 8 V (volts) positive pole output terminal of the battery pack 11 is connected to a 8 V positive pole terminal (8B+) of the smart battery 1. A 12 V positive pole output terminal of the battery pack 11 is connected to a 12 V positive pole terminal 12B+ of the smart battery 1. As output terminals of the smart circuit module 10, there are a positive pole output terminal (P+) connected to a 12 V positive pole terminal (12B+), a negative pole output terminal (Pxe2x88x92) connected to a negative pole terminal (Bxe2x88x92), a clock terminal C, a data terminal D, and a temperature terminal T.
In the battery pack 11, the first through seventh secondary batteries B1-B7 are sequentially stacked from the position of output terminals of a pack connected to power input terminals Bxe2x88x92, 8B+, and 12B+ of the smart circuit module 10. Positive pole terminals of the first through third secondary batteries B1, B2, and B3 are connected in common by a conductive body to the 12 V positive pole terminal 12B+ of the smart battery 1. Here, since the common connection portion of the positive pole terminals of the first through third secondary batteries B1, B2, and B3 occupy most of the conductive body, internal resistance of the conductive body is not so high to need consideration in relation with the current paths. Also, negative pole terminals of the first through third secondary batteries B1, B2, and B3 and positive pole terminals of the fourth through sixth secondary batteries B4, B5, and B6 are connected in common by a conductive body to the 8 V positive pole terminal 8B+ of the smart circuit module 10. Here, since the common connection portion of the negative pole terminals of the first through third secondary batteries B1, B2, and B3 and the positive pole terminals of the fourth through sixth secondary batteries B4, B5, and B6 occupy most of the conductive body, internal resistance of the conductive body is not so high to need consideration in relation with the current paths.
The ninth and eighth secondary batteries B9 and B8 are sequentially disposed from the positions of the output terminals of the pack in a row in a direction perpendicular to a direction in which the first through seventh secondary batteries B1-B7 are arranged. Positive pole terminals of the ninth and eighth secondary batteries B9 and B8, negative pole terminals of the fourth through sixth secondary batteries B4, B5, and B6, and a positive pole terminal of the seventh secondary battery B7 are connected in common by a second conductive body L2. Here, since the common connection portion of the negative pole terminals of the fourth through sixth secondary batteries B4, B5, and B6, and the positive pole terminal of the seventh secondary battery B7 occupy most of a vertical portion of the second conductive body L2, internal resistance of the vertical portion is not so high to need consideration in relation with the current paths. However, because a horizontal portion of the second conductive body L2 is not so, internal resistance of the horizontal portion has a great effect in relation with the current paths. Meanwhile, negative pole terminals of the seventh, eighth, ninth secondary batteries B7, B8, and B9 are connected in common by a first conductive body L1. Here, most of the first conductive body L1 which is the longest than the other conductive bodies is disposed between a connection portion of the negative pole terminal of the ninth secondary battery B9 and a connection portion of the negative pole terminal of the eighth secondary battery B8. Accordingly, internal resistance of the first conductive body L1 has the greatest effect in relation with the current paths.
Referring to FIG. 3, the current path through which current flows from the 12 V positive pole terminal 12B+ of the smart circuit module 10 to the negative pole terminal Bxe2x88x92 can be branched to nine ways listed in Table 1.
In Table 1, the internal resistance of the first conductive body L2 is greater than that of the second conductive body L2. Thus, referring to Table 1, the resistance of the current path of the eighth secondary battery B8 is the highest, the resistance of the current path of the seventh secondary battery B7 is the second highest, the resistance of the current path of the ninth secondary battery B9 is the third highest, and the resistance of the current path of each of the remaining first through sixth secondary batteries B1-B6 is the lowest.
Accordingly, in the conventional battery pack 11 according to a simple internal wiring, charging/discharging performance of the eighth secondary battery B8 is the worst and the life span thereof is the shortest. Therefore, performance of the smart battery 1 including the battery pack 11 is low and the life span thereof is reduced.
To solve the above-described and other problems, it is an object of the present invention to provide a battery pack in which the current characteristics of internal batteries are equalized so that the charging/discharging performance and life span thereof is improved.
It is another object to have a battery pack that is easy and inexpensive to manufacture.
To achieve the above and other objects, there is provided a battery pack in which first through nth secondary batteries, where n is an integer which is 2 or more, are sequentially stacked from the pack output terminals, (n+2)th and (n+1)th secondary batteries are disposed from the positions of pack output terminals in a row in a direction perpendicular to a direction in which the first through nth secondary batteries are arranged, first polarity terminals of the (n+2)th and (n+1)th secondary batteries are connected with each other, and a pack output terminal having a second polarity opposite to the first polarity and the second polarity terminals of the nth, the (n+1)th, and the (n+2)th are connected in common by a conductive body, wherein the second polarity terminals of the (n+2)th and (n+1)th secondary batteries are connected with each other by a first conductive body, a second conductive body is connected to the pack output terminals having the second polarity are connected at a first branch point of the first conductive body, and the first branch point of the first conductive body is set to minimize a difference between resistance values of current paths of the (n+2)th and (n+1)th secondary batteries between the pack output terminals having the first and second polarities.
According to the battery pack of the present invention, the difference between the resistance values of the current paths of the secondary batteries between the pack output terminals can be minimized. Accordingly, as the current characteristics of the secondary batteries are equalized, the charging/discharging (charging or discharging or both charging and discharging) performance and the life span thereof can be improved.
It is preferred in the present invention that a third conductive body is connected to the second polarity terminal of the nth secondary battery at a second branch point of the first conductive body, and the second branch point of the first conductive body is set to minimize a difference between resistance values of current paths of the (n+1)th and nth secondary batteries between the pack output terminals having the first and second polarities. Thus, the difference between the resistance values of the current paths of the secondary batteries between the pack output terminals having the first and second polarities can be further minimized.